Tom, Roger that. 7.62X54 is an awsome caliber. I dont know of a semi-auto in carbine length though (what a muzzle flash that'd have!). If I found one I'd own it that day!
Wheelgun, Quaker, Verify if barrel temp is effecting your groups. If thats it the rubber donut probably isnt going to do to much good. Look into cryo treating. It can make a BIG difference! Call around to local machine shops and ask where they get stuff "stress relieved". Then ask that place if they can do cryogenic treating. They'll usually do a barrel fairly cheap, especially if you get more than one done.
Midway sells the Limbsaver donuts, Basspro, Cabelas, Dunhams, Gander Mountain, about all the sporting goods shops have em.